The present invention relates to a vehicular lighting device which employs a large number of light-emitting diodes as light sources.
A conventional high-mount stop lamp or the like, which is mounted high on the rear portion of the body of a motor vehicle and is lit during braking of the vehicle, includes a large number of light-emitting diodes as light sources as shown in FIG. 1. The stop lamp includes a base 1, a face lens 2 covering the interior opening of the base 1, a printed circuit board 3 disposed inside the base 1, light-emitting diodes 4 juxtaposed on the printed circuit board 3 at prescribed intervals P in the direction of the width of the body, and light control portions 5 formed on the inside surface of the face lens and corresponding in position to respective ones of the diodes, whereby the rays of light emitted from the diodes are directed in prescribed directions by the light control portions.
However, since the interval P.sub.0 between the light control portions 5 of the conventional stop lamp is constant throughout the length of the stop lamp and the face lens 2 has a prescribed curvature, the distance L between each light-emitting diode 4 and the light control portion corresponding thereto differs along the length of the lamp with the distance being a maximum at the center of the lens and gradually decreasing toward the two ends thereof. For this reason, although the angles of diffusion .alpha. of the light from the diodes 4 are equal to each other, the areas of the lens 2 irradiated with the rays of light from the respective diodes differ from diode to diode. As a result, the light is not effectively used for illumination.
As shown in FIG. 2, since the irradiated area becomes larger as the distance L between the diodes 4 and corresponding light control portions 5 increases, some 6 of the light emitted from the diodes 4 irradiates the adjacent light control portions 5. If the distance L between the light-emitting diodes 4 at both ends of the stop lamp and the corresponding light control portions 5 diode is set at an optimal value chosen so as to prevent the light 6 from irradiating the adjacent light control sections, the distance between the light-emitting diode at the center of the stop lamp and the light control portion corresponding to that diode is large, and consequently a large portion of the light 6 from the center diode irradiates the adjacent light control portions.
Moreover, since each of the light control portions 5 must be designed so that just the rays of light from the corresponding diode 4 are directed in a designated direction, the light control portions cannot function effectively for the light 6 from the adjacent diodes. Therefore, the light from the diodes 4 is not effectively used for illumination.
On the other hand, if the distance L between the light-emitting diode 4 at the center of the stop lamp and the corresponding light control portion is set at a value so as to prevent the light from the diode irradiating the adjacent light control portions, the irradiated area of the face lens 2 decreases toward the ends of the stop lamp, and hence dark stripes are formed between the light control portions. In this case too the light from the light-emitting diodes is not effectively used. The problem becomes more serious as the curvature of the face lens 2 is increased.